1. Field of the Invention
For introducing fuel into direct-injection internal combustion engines, stroke-controlled injection systems with a high-pressure reservoir (common rail) are used, as are unit fuel injector systems or pump-line-nozzle systems. In fuel injection systems with a common rail, the injection pressure can advantageously be adapted to the load and rpm of an engine over wide operating ranges. To reduce emissions and to attain a high specific performance, a high injection pressure is necessary. The attainable pressure level in high-pressure fuel pumps is limited for reasons of strength, so that to further increase the pressure in fuel injection systems, pressure amplifiers in the fuel injectors are employed.
2. Description of the Prior Art
German Patent Disclosure DE 101 23 913 A1 discloses a fuel injection system for internal combustion engines with a fuel injector that can be supplied from a high-pressure fuel source. A pressure booster device having a movable pressure booster piston is connected between the fuel injector and the high-pressure fuel source. The pressure booster piston divides a chamber, which can be made to communicate with the high-pressure fuel source, from a high-pressure chamber that communicates with the fuel injector. For filling a differential pressure chamber of the pressure booster device with fuel or evacuating the differential pressure chamber of fuel, the fuel pressure in the high-pressure chamber can be varied. The fuel injector has a movable closing piston for opening and closing injection openings. The closing piston protrudes into a closing-pressure chamber, so that the closing piston can be acted upon by fuel pressure to attain a force acting in the closing direction on the closing piston. The closing-pressure chamber and the differential pressure chamber are formed by a common closing-pressure differential pressure chamber, and all the portions of the closing-pressure differential pressure chamber communicate permanently with one another from exchanging fuel. A pressure chamber is provided for supplying the injection openings with fuel and for subjecting the closing piston to a force acting in the opening direction. A high-pressure chamber communicates with the high-pressure fuel source in such a way that aside from pressure fluctuations, at least the fuel pressure of the high-pressure fuel source can be applied constantly to the high-pressure chamber; the pressure chamber and the high-pressure chamber are formed by a common injection chamber. All the portions of the injection chamber communicate permanently with one another for exchanging fuel.
German Patent Disclosure DE 102 47 903.8 A1 discloses a pressure-amplified fuel injection system with an internal control line. The fuel injection system, which communicates with a high-pressure source, has a multi-part injector body. In it, a pressure booster that can be actuated via a differential pressure chamber is received, and its pressure booster piston divides a work chamber from the differential pressure chamber. The fuel injection system is actuatable via a switching valve. A change in pressure in the differential pressure chamber of the pressure booster is effected via a central control line, which extends through the pressure booster piston. The central control line is passed through the work chamber of the pressure booster and is sealed off from it via a high-pressure-proof connection.
German Patent Disclosure DE 196 11 884 A1 relates to a fuel injection valve for internal combustion engines. It includes a pistonlike valve member that is axially displaceable in a bore of a valve body. This valve member, on its end toward the combustion chamber, has a valve sealing face, which to open an injection cross section cooperates with a valve seat provided on the end of the bore toward the combustion chamber. Moreover, the valve member has a pressure shoulder, pointing in the direction of the valve sealing face, by means of which shoulder the valve member is subdivided into a larger-diameter guide part guided slidingly in the bore and a smaller-diameter free shaft part. A pressure chamber formed by a cross-sectional expansion of the bore is provided, which communicates with the valve seat via a gap formed between the free shaft of the valve member and the wall of the bore and which is adjoined, on the end facing away from the valve seat, by a guide portion of the bore that receives the guide part of the valve member. The valve body is penetrated by a pressure conduit, which discharges radially outward of the bore into the end of the pressure chamber facing away from the valve seat. The pressure shoulder on the valve member constantly plunges so far into the guide portion of the bore that an annular gap remains between the valve member and the wall of the bore on the end of the guide portion of the bore adjacent to the pressure chamber. In this gap, a contrary force on a remaining web between the bore and the pressure conduit is built up.
In previous version of pressure amplifiers controlled via the differential pressure chamber, the differential pressure chamber communicates, through what is as a rule a horizontal bore, with a second, valve-carrying bore. The horizontal bore proves to be extremely difficult to make. Time-consuming, expensive processes such as electrochemical countersinking or erosion must be employed. Moreover, at the intersection points between the differential pressure chamber and the horizontal bore, the maximum stresses occur in the component. High surface quality and rounding off of the edges that necessarily occur in manufacture, given the desired system pressures that must still be increased further, no longer suffice to obtain durable components. The internal central control line known from DE 102 47 903 A1 requires greater effort and expense of production and assembly than simple bores inside the injector body.